The fact that some cases of hypertension are resistant to treatment by pure pharmacological means has reignited the use of invasive techniques in treating these cases. Historically, surgical renal denervation was the prominent treatment for severe cases of hypertension prior to the introduction of orally administered anti-hypertensive drugs (Smithwick and Thompson, 1953). This type of conventional surgery was, however, extremely invasive and involved a major surgical procedure which greatly limits it practicality (DiBona, 2003). At least two clinical studies have, to a certain extent, provided support to the use of minimally invasive catheter-based radiofrequency (RF) renal nerve ablation in the treatment of resistant hypertension (Krum et al., 2009; Esler et al., 2009). Patients with hypertension resistant to the available anti-hypertensive drugs were selected for these studies and this interventional procedure demonstrated a 89% clinical success rate in lowering their blood pressure in a small and very selective patient population.
While there is growing interest in using such minimal invasive interventional techniques for treatment of hypertension, all systems on the market, including the Ardian Symplicity® Catheter System, are not optimally designed for this purpose. There are apparent shortcomings, even in the Ardian Symplicity® Catheter System, that limit the certainty of the interventional outcome.
An important aspect not considered in the current interventional systems and techniques, is the precision and accuracy in locating and delivering an effective dose of energy to a suitable ablation spot in the arterial wall. The current commonly accepted procedures for performing renal nerve ablation via catheters typically consists the steps of administering to the arterial wall 4 to 6 ablations, each made by 2 minutes of RF energies and spaced both longitudinally and rotationally along the inner wall of each renal artery. The ablations had to be delivered “blindly” in this helical manner because the exact location of the nerves innervating the renal artery with respect to the ablation catheter is unknown before and during the delivery of the ablation energy. An inaccurately directed dose of energy not only causes unnecessary damage to healthy tissues and non-sympathetic nerves but more importantly could not provide the promised solution for hypertension which the interventional procedure was intended for. In fact, in certain clinical settings other than the two published studies, the responder rate of the current “blind” type of interventional procedure could go as low as 50% (Medical devices: pg 1-2, Feb. 22, 2012).
Theoretically, precise nerve ablation in the wall of an artery could be achieved by mapping the location of the nerves innervating the arterial wall prior to delivery of the dose of energy. By monitoring physiological parameters associated with the autonomic nervous systems such as the blood pressure, heart rate and muscle activity while a stimulus is delivered to a selected location on the arterial wall, the presence of autonomic nerves in the immediate vicinity of this location will be reflected from the changes in the monitored physiological parameters (Wang, US 2011/0306851 A1).
Further, the sympathetic and parasympathetic nerves of the autonomic nervous system often exert opposite effects in the human body including their control on blood pressure and heart rate. While ablation of the sympathetic nerves innervating the arterial walls will relieve hypertension, there is an equally possible chance that other tissues such as parasympathetic nerves are ablated in the “blind” type of interventional procedure. The result for decreasing or removal of nerve activity blindly may worsen the hypertension as could be inferred from several animal studies (Ueda et al., 1967; Beacham and Kunze, 1969; Aars and Akre, 1970; Ma and Ho, 1990; Lu et al. 1995).
The cause of failure in the current treatment was attributed to regeneration of the nerves after the ablation (Esler et al., 2010) and may also be related to both the inability to deliver the dose of energy to the targeted nerve and an insufficient dose of energy delivered for effective ablation. At present, the success of renal denervation is only assessed by the measurement of a secondary effect known as norepinephrine spillover at least days after the interventional procedure (Krum et al., 2009) and lack a method for immediate post-procedural assessment. In order to improve the success rate of the interventional procedure, it is important to not only locate suitable ablation spots on the arterial wall, but also ensure that the energy is precisely and accurately delivered to a targeted nerve during the ablation process, and confirm immediately after the ablation that the dosage of energy delivered has effectively ablated the targeted nerve.
In response to the shortcomings of the current system and methods for nerve ablation, the present invention introduces improvements by providing a system and methods for accurate and precise location of suitable ablation spots on a renal arterial wall; ensuring sufficient ablation energy is accurately directed into a targeted nerve and to conduct immediate post-procedural assessment of nerve ablation.